Element-selective and time-resolved magnetic investigations in the extreme ultraviolet range

Grychtol, Patrik

Book	PreJuSER-136289

Element-selective and time-resolved magnetic investigations in the extreme ultraviolet range

Grychtol, P. (Corresponding author)FZJ*

2011
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-706-1

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / key technologies 22, XII, 144 S. (2011) = Universität Duisburg, Diss., 2011

Please use a persistent id in citations: http://hdl.handle.net/2128/4387

Abstract: The objective of this thesis is to explore the potential of the extreme ultraviolet (EUV) region to serve as an element-selective and magnetic contrast mechanism for magnetooptical investigations. To this end, the following work focuses on alloy and multilayer model systems based on iron, cobalt and nickel due to their high relevance for both xfundamental research and technology. Four reectivity experiments exploiting the transversal magneto-optical Kerr effect (T-MOKE) have been performed by tuning the photon energy to the $\textit{M}$ absorption edges of the respective 3d transition ferromagnets and by employing synchrotron as well as laser based soft x-ray light sources. In the first experiment spatially separated but homogeneous and ferromagnetically coupled layers in a wedged Co(5 nm)/Si(1-4 nm)/Ni(8 nm)/Fe(2 nm) multilayer are studied, whereas the second experiment is concerned with magneto-optical investigations of a single Ni$_{80}$Fe$_{20}$(5 nm)/Cr(0.6 nm)/Co$_{40}$Fe$_{60}$(10 nm) multilayer containing two anti-ferromagnetically coupled heterogeneous ferromagnetic layers. Measurements and supporting simulations of the magneto-optical response as a function of the photon energy, the incidence angle and the spacer thickness explore the character of the magneto-dichroic signal in the EUV and its potential for layer-selective investigations. A magnetic contrast as high as 80% can be obtained and the recorded hysteresis loops prove that the switching of single layers can indeed be measured layer-selectively. In the third experiment, precessional dynamics of the magnetization in thin permalloy films patterned to form a coplanar waveguide is induced by ultrashort laser pulses. The resulting oscillatory response is probed by synchronized EUV pulses originating from a synchrotron tuned to the $\textit{M}$ absorption edge of Ni. The obtained results in combination with reference measurements in the visible range not only prove the feasibility, but also explore the limitations of this pump-probe approach. The fourth experiment is concerned with the ultrafast demagnetization of permalloy, which is optically driven by intense laser pulses. A magnetic contrast of 30% can be exploited to element-selectively probe the evolution of the magnetic system by EUV pulses from a table-top soft x-ray source with an unprecedented temporal resolution. The result suggests that the local spin environment at the atomic level plays a vital role in the dynamic response of magnetic materials, and must be included for a complete understanding of the microscopic physics underlying demagnetization processes.

Keyword(s): Kerr effect ; far UV radiation ; synchrotron radiation ; magnetooptics ; resistive switching ; hysteresis